The Viaduct Works' Handbook
Forfatter: Henry N. Maynard
År: 1868
Forlag: E. And F. N. Spon
Sted: London
Sider: 108
UDK: 624.3
Being A Collection Of Examples From Actual Practice Of Viaducts, Bridges, Roofs, And Other Structures In Iron; Together With Tables Of Prices, Weights, And Other Information Useful To Engineers In Design And Estimating Wrought And Cast-Iron Work
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21
It will be noticed, in comparing the weights, that the bridges
for Italy are much heavier than for some other countries. This is
chiefly in consequence of the Government regulation of that country
for iron bridges requiring that the metal should not be strained over
4 tons per square inch either in tension or compression; and hence
they are made stronger than those for Spain and Portugal.
Tn all the foregoing examples of lattice bridges it will be seen
that the lattices formed by the struts and ties, between the com-
pression and tension bars, are placed at an angle of 60. Many
engineers adopt other forms of lattice girders; whilst some prefer
placing the lattices at an angle of 45°: others, of various angles,
making them also of tighter section, and placed nearer together, form-
ing trellis-work more approaching the principle of a plate girder.
From a careful comparison of the numerous examples which have
come under the notice of the writer, it appears to show that, as
regards economy, there is no great difference; for where a saving of
iron is effected, it is generally attended with the employment of more
expensive sections of material and labour in making.
Light trellis girders are sometimes economical and convenient for
small foot bridges, &c., where they are employed to form a parapet,
as well as to carry the weight, as in the accompanying sketch.
From amongst the numerous lattice and trellis bridges made at
the Viaduct Works, designed by various engineers, are selected the
following particulars:—________________________________________
Number of Spans. Length of Span in feet. Total weight. Description and Remarks.
5 120 275 (Lattice 45°; no cross girders; 8 in. wood floor, road 1 top. (Tees.) (Trellis bars about 1 foot apart, angle 45°; no cross girders;
12 70 240 1 the road supported on wood cross bearers. (Spain.)
21 74 450 Ditto ditto.
4 98 120 Road top; no cross girders; single line. Solway—Single line railway, latticed at angle 40.
180 30 1500
5 176 to 202 2700 Thames, at Blackfriars—For 4 lines railway; trellis.